The present invention relates to an electric charge-reading and injection device. It also relates to the application of such a device to charge-transfer devices which comprise one or more filters or delay lines.
In numerous charge-transfer devices, it is necessary to read a quantity of electric charges then to inject into the device a quantity of charges which depends on the quantity of charges previously read.
This is the case for example with recursive filters where the quantity of charges injected into the filter is equal to the difference between the quantity of charges corresponding to the signal to be processed and the quantity of charges previously read.
Recursive filters of the prior art generally have a charge-reading device, such for example as the one described in French patent application No. 77 13 857, published under the number 2.839.899, in the name of THOMSON-CSF; this reading device converts the charges into an electric signal, either a current, or a voltage, which is fed to the negative input of a differential amplifier, connected to the input of the filter, which receives at its positive input the signal to be processed.
Recursive filters of the prior art present numerous drawbacks, among which may be mentioned:
the fact that the charge-reading device and the differential amplifier have an inherent gain which must be adjusted so as to inject into the filter a quantity of charges corresponding exactly to the difference between the quantity of charges corresponding to the signal to be processed and the quantity of charges previously read;
the space taken up by the charge-reading device and the differential amplifier which it is not always possible to integrate on the same substrate as the filter properly speaking, their high consumption for they generally comprise MOS transistors whose consumption is very much greater than that of the charge-transfer devices and finally the non-linearities likely to be introduced by the MOS transistors.
When several transversal filters are placed in series so as to obtain a frequency pattern with high rejection, or several delay lines, it is also necessary to read the charges at the output of each filter or each delay line then to inject the quantity of charges read in the following filter or delay line.
In the prior art, there is inserted between two filters or two delay lines a charge-reading device which presents the above-mentioned drawbacks of space taken up, consumption and non-linearity in particular.